https://developers.google.com/search/docs/guides/intro-structured-data

Structured data refers to kinds of data with a high level of organization, such as information in a relational database. When information is highly structured and predictable, search engines can more easily organize and display it in creative ways. Structured data markup is a text-based organization of data that is included in a file and served from the web. It typically uses the schema.org vocabulary—an open community effort to promote standard structured data in a variety of online applications.

Structured data markup is most easily represented in JSON-LD format, which stands for JavaScript Object Notation for Linked Data. The following is a simple JSON-LD structured data example you might use for contact information for your company:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": "Organization",
  "url": "http://www.your-company-site.com",
  "contactPoint": [{
    "@type": "ContactPoint",
    "telephone": "+1-401-555-1212",
    "contactType": "customer service"
  }]
}
</script>

Structured data markup describes things on the web, along with their properties. For example, if your site has recipes, you could use markup to describe properties for each recipe, such as the summary, the URL to a photo for the dish, and its overall rating from users.

Introduction to Structured Data